Abstract The advent of combination antiretroviral therapy (cART) has largely eliminated the incidence of encephalitis-like in- ?ammation in human immunode?ciency virus-1 (HIV-1) patients; however, HIV-1-associated neurocognitive disorder (HAND) persists in virologically suppressed patients. HAND is observed in 50% of HIV-1-infected individuals in coun- tries with widespread access to cART [8]. Recent data obtained from humanized mouse models of HIV-1 infection indi- cate that tissue macrophages are a long-lived HIV-1 reservoir even under ef?cacious cART [2, 3], suggesting that tissue macrophages, including microglia and splenic macrophages, can drive chronic in?ammation in their resident tissues. Concurrently, next-generation sequencing technologies have vastly expanded our knowledge of factors that regulate the development and homeostasis of tissue macrophages (e.g., microglia, splenic macrophages, etc) [9, 10, 11], permitting an examination of their relevance to disease processes. Among these is the master regulator transcription factor Mafb, which has been shown to contribute to the expression of tissue macrophage-associated transcripts [12] as well as the repression of anti-viral and immune-related genes [11]. My preliminary data shows that Mafb overexpression in the BV2 microglial cell line upregulates the tissue macrophage-associated transcripts Mertk and C1qa, while significantly reducing TNF-a and CCL4 production in response to stimulation with HIV-1 Tat. The primary goal of this proposal is to determine mechanistically how Mafb suppresses pro-in?ammatory signaling in microglia and whether the MLK3 inhibitor URMC-099 promotes the stability of the Mafb protein under in?ammatory conditions. To this end, I propose two aims. First, I will use an inducible CRISPR/Cas9-based activation (CRISPRa) approach to titrate Mafb expression in BV2 mouse microglia and in C20 human microglia cell lines to determine whether Mafb gene dosage is inversely correlated TNF-a and CCL4 expression at both the mRNA and protein levels. I will determine whether Mafb acts as a transcriptional suppressor at these loci using chromatin immunoprecipitation in Mafb-overexpressing microglia and lu- ciferase reporter assays in HEK293T cells. Second, I will determine whether inhibition of c-Jun N-terminal kinase (JNK) prolongs the half-life of Mafb protein following HIV-1 Tat stimulation of microglia in vitro and in tissue macrophages (including microglia and splenic macrophages) in vivo using HIV-1 infected humanized NOD/SCID/IL2Rgc-/- (hNSG) mice. Altogether, the proposed experiments will identify key roles for Mafb in de?ning features of tissue macrophage physiology, particularly within the context of chronic HIV-1 infection. Accomplishment of these goals may also inform therapeutic strategies for a wide variety of in?ammatory conditions in which tissue macrophages contribute to collateral tissue damage and worsened disease outcomes.